Composite dielectric forming methods and composite dielectrics

ABSTRACT

A composite dielectric forming method includes atomic layer depositing alternate layers of hafnium oxide and lanthanum oxide over a substrate. The hafnium oxide can be thermally stable, crystalline hafnium oxide and the lanthanum oxide can be thermally stable, crystalline lanthanum oxide. A transistor may comprise the composite dielectric as a gate dielectric. A capacitor may comprise the composite dielectric as a capacitor dielectric.

TECHNICAL FIELD

The present invention pertains to composite dielectric forming methodsas well as composite dielectrics, including those formed by thedescribed method. In particular, the invention pertains to compositedielectrics containing both hafnium oxide and lanthanum oxide.

BACKGROUND OF THE INVENTION

Increasing the performance of integrated circuits (ICs), both withregard to more complex functionality and higher speeds, is a primarygoal of efforts in advancing the semiconductor arts. One method that hasbeen extensively employed to achieve this goal is scaling, that is,decreasing area or size of individual device components that are used toform such integrated circuits. For example, the gate width of a typicalMOS transistor has been reduced over the past several years from severalmicrons to fractions of a micron and gate widths of 0.1 micron or lessmay soon be desired. Such scaling efforts have also effected the size ofcapacitors used in a variety of ICs such as DRAMS and SRAMS (dynamic andstatic random access memories, respectively).

While such scaling efforts have resulted in the desired increases inperformance, generally such size reductions also impact at least somecharacteristics of the devices so “scaled.” For example, reducing thegate width of a transistor generally reduces the transistor's output anddecreasing the size of a capacitor generally reduces the capacitance oramount of charge such a capacitor can store. As transistor gate width isreduced, the gate dielectric layer thickness can also be reduced to atleast partially compensate for the change in device output. Similarly,as the size of capacitor structures is reduced, materials such ashemispherically grained polysilicon (HSG) can be employed to increasethe effective surface area of such structures and compensate, at leastin part, for such size reductions.

Silicon dioxide (SiO₂), with a dielectric constant of about 3.9, remainsthe most common material employed for gate dielectric layers. Tomaintain transistor output at an acceptable level, a transistor having agate width of 0.1 micron can use an ultra-thin SiO₂ layer with athickness of about 2 nanometers (nm). Ultra-thin being defined herein asa thickness of about 5 nm or less.

The forming and use of such ultra-thin SiO₂ layers is problematic for avariety of reasons since such layers consist of only a few layers ofmolecules. Thus only one additional or missing layer of molecules canhave a dramatic effect on device performance. One method of reducingthese problems is the use of a thicker layer of an alternativedielectric material such as a metal oxide having a higher dielectricconstant than that of SiO₂. For the purpose of illustration, a metaloxide gate dielectric having an appropriately high dielectric constantcan be formed with a thickness several times that of a SiO₂ layer whilehaving the performance characteristics of the thinner SiO₂ layer. Thusthe thicker metal oxide layer is said to have the equivalent oxidethickness (EOT) of the thinner layer. Alternate metal oxide materialssuch as titanium oxide (TiO₂), aluminum oxide (Al₂O₃), tantalum oxide(Ta₂O₅) and others have therefore received attention as replacements forSiO₂. However, such alternate materials preferably additionally exhibita large band-gap with a favorable band alignment, good thermalstability, and the ability to be formed in a manner consistent withknown semiconductor process methods at reasonable cost and yield.

Unfortunately, many candidate metal oxide materials having anappropriately high dielectric constant, do not meet these additionalrequirements. Thus it is desirable to provide alternate dielectricmaterials and methods of forming such materials that are appropriate asa replacement for SiO₂.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a composite dielectric formingmethod includes atomic layer depositing alternate layers of hafniumoxide and lanthanum oxide over a substrate. As an example, the hafniumoxide can include thermally stable, crystalline hafnium oxide and thelanthanum oxide can include thermally stable, crystalline lanthanumoxide.

In another aspect of the invention, a composite dielectric formingmethod includes chemisorbing at least one monolayer of a first materialover a substrate, the first material containing a first metal, andtreating at least some of the chemisorbed first material, forming anoxide of the first metal. The method includes chemisorbing on the firstmetal oxide at least one monolayer of a second material containing asecond metal and treating at least some of the chemisorbed secondmaterial, forming an oxide of the second metal. One of the first andsecond metals includes hafnium and the other includes lanthanum. As anexample, the first material includes HfCl₄. Alternatively, the firstmaterial can include La(thd)₃. Treating the chemisorbed first materialcan include exposure to H₂O.

According to a further aspect of the invention, a composite dielectricforming method includes atomic layer depositing a first material on asubstrate using a first precursor containing a first metal, exposing thedeposited first material to oxygen, and forming an oxide of the firstmetal. The method includes atomic layer depositing a second material onthe first metal oxide using a second precursor containing a secondmetal, exposing the deposited second material to oxygen, and forming anoxide of the second metal. One of the first and second metals includeshafnium and the other includes lanthanum.

In a still further aspect of the invention, a composite dielectricincludes alternate monolayers of hafnium oxide and lanthanum oxide overa substrate. As an example, the composite dielectric can include aplurality of single hafnium oxide monolayers interspersed among aplurality of single lanthanum oxide monolayers. Alternatively, thecomposite dielectric can include a plurality of hafnium oxidemultilayers interspersed among a plurality of lanthanum oxidemultilayers, the multilayers including multiple monolayers.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a partial sectional view of a transistor construction at anintermediate process stage according to one aspect of the invention.

FIG. 1A is an enlarged view of a portion of the transistor constructionshown in FIG. 1.

FIG. 2 is a partial sectional view of a transistor construction at aprocess stage subsequent to that shown in FIG. 1.

FIG. 2A is an enlarged view of a portion of the transistor constructionshown in FIG. 2.

FIG. 3 is a partial sectional view of a transistor construction at aprocess stage subsequent to that shown in FIG. 2.

FIG. 4 is a partial sectional view of a transistor construction at aprocess stage subsequent to that shown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Material properties of various high-K dielectric materials for gatedielectrics are discussed in a recent article by G. D. Wilk, et al.,High-K Gate Dielectric: Current Status and Materials PropertiesConsiderations, Journal of Applied Physics, vol. 89, no. 10, pp.5243-5275 (May, 2001). Table 1 summarizes information from Wilk et al.TABLE 1 Dielectric Band gap Δ E_(C) (eV) Crystal Material Constant (K)E_(G) (eV) to Si Structure(s) SiO₂ 3.9 8.9 3.2 Amorphous Si₃N₄ 7 5.1 2Amorphous Al₂O₃ 9 8.7 2.8 Amorphous Y₂O₃ 15 5.6 2.3 Cubic La₂O₃ 30 4.32.3 Hexagonal, cubic Ta₂O₅ 26 4.5 1-1.5 Orthorhombic TiO₂ 80 3.5 1.2Tetragonal (rutile, anatase HfO₂ 25 5.7 1.5 Monoclinic, tetragonal,cubic ZrO₂ 25 7.8 1.4 Monoclinic, tetragonal, cubic

The inventors recognized the advantage of a composite dielectriccontaining hafnium oxide and lanthanum oxide as described in U.S. patentapplication Ser. No. 09/881,408, filed Jun. 13, 2001, entitled ADielectric Layer Forming Method And Devices Formed Therewith, thesubject matter of which is incorporated herein by reference for itspertinent and supportive teachings. However, improved performancecharacteristics can be achieved with the composite dielectrics describedherein that also include hafnium oxide and lanthanum oxide.

Hafnium dioxide (HfO₂) is a dielectric material having a relatively highrefractive index of 25 and a wide band gap of 5.7 electron volts (eV).For this reason, the material may be used in optical coatings. Further,hafnium dioxide may be used in protective coatings because of itsthermal stability and hardness. At about 20° C. (room temperature) andabout 1 atmosphere pressure (atmospheric pressure), pure hafnium dioxidetends to appear in the monoclinic phase. However, hafnium dioxide cancrystallize in different forms (form polymorphs) that are more hardand/or dense than the monoclinic phase. For example, a tetragonal phaseof hafnium dioxide has been observed at high pressure and reported toexhibit a hardness comparable to that of diamond.

The tetragonal phase, as well as orthorhombic hafnium dioxide alsoformed at high pressure, may be quenched to atmospheric pressure. A hightemperature cubic phase has further been observed in thin film grown byoxidation of hafnium and annealing at 500 to 600° C. Tetragonal and/ororthorhombic phases of hafnium dioxide can also be formed by atomiclayer deposition (ALD). Such polymorphs are normally consideredmetastable, but might be stabilized in ALD thin films due to sizeeffects and/or intrinsic strains. The contribution of both these factorsappears to increase with decreasing film thickness. Accordingly, thinfilm growth methods allowing precise control of film thickness may beused to study and achieve stabilization of various hafnium dioxidecrystalline structures.

ALD of La₂O₃ thin films has also been accomplished between 180 to 425°C. on soda-lime glass and (100) silicon substrates at a reduced pressureof 2 to 3 millibar. Accordingly, an expectation exists that metastableor even stable La₂O₃ may be formed by ALD as well.

Atomic layer deposition (ALD) involves formation of successive atomiclayers on a substrate. Such layers may comprise an epitaxial,polycrystalline, amorphous, etc. material. ALD may also be referred toas atomic layer epitaxy, atomic layer processing, etc. Further, theinvention may encompass other deposition methods not traditionallyreferred to as ALD, for example, chemical vapor deposition (CVD), pulsedCVD, etc., but nevertheless including the method steps described herein.The deposition methods herein may be described in the context offormation on a semiconductor wafer. However, the invention encompassesdeposition on a variety of substrates besides semiconductor substrates.

In the context of this document, the term “semiconductor substrate” or“semiconductive substrate” is defined to mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductive substrates describedabove.

Described in summary, ALD includes exposing an initial substrate to afirst chemical specie to accomplish chemisorption of the specie onto thesubstrate. Theoretically, the chemisorption forms a monolayer that isuniformly one atom or molecule thick on the entire exposed initialsubstrate. In other words, a saturated monolayer. Practically, asfurther described below, chemisorption might not occur on all portionsof the substrate. Nevertheless, such an imperfect monolayer is still amonolayer in the context of this document. In many applications, merelya substantially saturated monolayer may be suitable. A substantiallysaturated monolayer is one that will still yield a deposited layerexhibiting the quality and/or properties desired for such layer.

The first specie is purged from over the substrate and a second chemicalspecie is provided to react with the first monolayer of the firstspecie. The second specie is then purged and the steps are repeated withexposure of the second specie monolayer to the first specie. In somecases, the two monolayers may be of the same specie. As an option, thesecond specie can react with the first specie, but not chemisorbadditional material thereto. That is, the second specie can cleave someportion of the chemisorbed first specie, altering such monolayer withoutforming another monolayer thereon. Also, a third specie or more may besuccessively chemisorbed (or reacted) and purged just as described forthe first and second species.

Purging may involve a variety of techniques including, but not limitedto, contacting the substrate and/or monolayer with a carrier gas and/orlowering pressure to below the deposition pressure to reduce theconcentration of a specie contacting the substrate and/or chemisorbedspecie. Examples of carrier gases include N₂, Ar, He, etc. Purging mayinstead include contacting the substrate and/or monolayer with anysubstance that allows chemisorption byproducts to desorb and reduces theconcentration of a contacting specie preparatory to introducing anotherspecie. The contacting specie may be reduced to some suitableconcentration or partial pressure known to those skilled in the artbased on the specifications for the product of a particular depositionprocess.

ALD is often described as a self-limiting process, in that a finitenumber of sites exist on a substrate to which the first specie may formchemical bonds. The second specie might only bond to the first specieand thus may also be self-limiting. Once all of the finite number ofsites on a substrate are bonded with a first specie, the first speciewill often not bond to other of the first specie already bonded with thesubstrate. However, process conditions can be varied in ALD to promotesuch bonding and render ALD not self-limiting. Accordingly, ALD may alsoencompass a specie forming other than one monolayer at a time bystacking of a specie, forming a layer more than one atom or moleculethick. The various aspects of the present invention described herein areapplicable to any circumstance where ALD may be desired. A few examplesof materials that may be deposited by ALD include hafnium oxide,lanthanum oxide, and others.

Often, traditional ALD occurs within an often-used range of temperatureand pressure and according to established purging criteria to achievethe desired formation of an overall ALD layer one monolayer at a time.Even so, ALD conditions can vary greatly depending on the particularprecursors, layer composition, deposition equipment, and other factorsaccording to criteria known by those skilled in the art. Maintaining thetraditional conditions of temperature, pressure, and purging minimizesunwanted reactions that may impact monolayer formation and quality ofthe resulting overall ALD layer. Accordingly, operating outside thetraditional temperature and pressure ranges may risk formation ofdefective monolayers.

The general technology of chemical vapor deposition (CVD) includes avariety of more specific processes, including, but not limited to,plasma enhanced CVD and others. CVD is commonly used to formnon-selectively a complete, deposited material on a substrate. Onecharacteristic of CVD is the simultaneous presence of multiple speciesin the deposition chamber that react to form the deposited material.Such condition is contrasted with the purging criteria for traditionalALD wherein a substrate is contacted with a single deposition speciethat chemisorbs to a substrate or reacts with a previously depositedspecie. An ALD process regime may provide a simultaneously contactedplurality of species of a type or under conditions such that ALDchemisorption, rather than CVD reaction occurs. Instead of reactingtogether, the species may chemisorb to a substrate or previouslydeposited specie, providing a surface onto which subsequent species maynext chemisorb or react to form a complete layer of desired material.Under most CVD conditions, deposition occurs largely independent of thecomposition or surface properties of an underlying substrate. Bycontrast, chemisorption rate in ALD might be influenced by thecomposition, crystalline structure, and other properties of a substrateor chemisorbed specie. Other process conditions, for example, pressureand temperature, may also influence chemisorption rate.

According to one aspect of the invention, a composite dielectric formingmethod includes ALD of alternate layers of hafnium oxide and lanthanumoxide over a substrate. The hafnium oxide can include thermally stable,crystalline hafnium oxide. The lanthanum oxide can include thermallystable, crystalline lanthanum oxide. It is an advantage of the variousaspects of the invention described herein that ALD allows formation ofmetastable or stable crystalline structures. As indicated above, theappearance of metastable hafnium dioxide polymorphs in thin filmsprovides evidence that such crystalline phases may be stabilized as aresult of size effects and/or intrinsic strains. The contribution ofthese factors apparently increases with decreasing film thickness.

Accordingly, atomic layer deposition wherein film thickness can beprecisely controlled provides optimum circumstances for stabilizingcrystalline phases of hafnium oxide and lanthanum oxide. The method caninclude forming one hafnium oxide monolayer, forming one lanthanum oxidemonolayer, and repeating to form a plurality of single hafnium oxidemonolayers interspersed among a plurality of single lanthanum oxidemonolayers. With each monolayer of hafnium oxide formed one moleculethick, the likelihood of stabilization is maximized.

However, a suitable composite dielectric may be formed withoutmaximizing the likelihood of stabilization. Accordingly, the method alsoincludes separately forming multiple hafnium oxide monolayers creating ahafnium oxide multilayer, separately forming multiple lanthanum oxidemonolayers creating a lanthanum oxide multilayer, and repeating to forma plurality of hafnium oxide multilayers interspersed among a pluralityof lanthanum oxide multilayers. The number of hafnium oxide or lanthanumoxide monolayers formed as a part of each multilayer may be selected tocorrespond with the desired stability of the composite dielectric thusformed. As the number of monolayers comprised by a hafnium oxidemultilayer increases, the risk of thermal instability also increases.The same is true for lanthanum oxide.

However, the likelihood of instability may increase at a different ratefor hafnium oxide in comparison to lanthanum oxide for a given number ofmonolayers. Accordingly, it may be suitable to group a larger number ofmonolayers of one material into a multilayer while not suitable for theother material. Differing numbers of monolayers between hafnium oxideand lanthanum oxide may thus produce a composite dielectric comprising10-90 atomic percent (at. %) hafnium oxide and 10-90 at. % lanthanumoxide. Preferably, the composite dielectric includes 25-75 at. % hafniumoxide and 25-75 at. % lanthanum oxide, but most preferably approximately50 at. % of each. The hafnium oxide can include HfO₂ and the lanthanumoxide can include La₂O₃.

In accordance with the knowledge of those of ordinary skill now known orlater developed, the substrate temperature during ALD may influence theparticular crystalline phase assumed by the deposited material. HfO₂ isknown to form three crystal structures and La₂O₃ is known to form twocrystal structures, as described in Table 1 herein. Preferably,substrate temperature is from about 180° C. to about 425° C., or morepreferably from 250° C. to 400° C. Thus, substrate temperature may beselected to obtain a deposited material having a desired crystalstructure selected from among the structures listed in Table 1. It isconceivable that temperature may be altered such that different layersof the same compound exhibit different crystal structures.

According to another aspect of the invention, a composite dielectricforming method includes chemisorbing at least one monolayer of a firstmaterial over a substrate, the first material containing a first metal,and treating at least some of the chemisorbed first material, forming anoxide of the first metal. The method includes chemisorbing on the firstmetal oxide at least one monolayer of a second material containing asecond metal and treating at least some of the chemisorbed secondmaterial, forming an oxide of the second metal. One of the first andsecond metals includes hafnium and the other includes lanthanum. Thefirst material can include HfCl₄ and/or other hafnium-containingmaterials known to those skilled in the art. Instead, the first materialcan include La(thd)₃, where thd is 2,2,6,6-tetramethyl-3,5-heptanedione,and/or other lanthanum-containing materials known to those skilled inthe art. Treating the chemisorbed first material can include exposure toH₂O, and/or other materials known to those skilled in the art.

In a further aspect of the invention, a composite dielectric formingmethod includes ALD of a first material on a substrate using a firstprecursor containing a first metal, exposing the deposited firstmaterial to oxygen, and forming an oxide of the first metal. The methodincludes ALD of a second material on the first metal oxide using asecond precursor containing a second metal, exposing the depositedsecond material to oxygen, and forming an oxide of the second metal. Oneof the first and second metals includes hafnium and the other includeslanthanum.

In keeping with the concept of ALD described herein, a purge may beprovided after deposition of a material before exposure to oxygen aswell as after exposure to oxygen before another deposition step. Pulsingof a precursor during deposition and pulsing of oxygen during exposureto oxygen can both be about 2 seconds. Nitrogen (N₂) may be used as acarrier gas for precursors and oxygen as well as a purging gas andpreferably has a purity of greater than 99.999%. The pressure duringfilm deposition can be from about 2 to about 3 millibar. La(thd)₃ as aprecursor may be synthesized from 99.99% La₂O₃ according to methodsknown to those skilled in the art and then purified by sublimation.

FIG. 1 shows a partial cross-sectional view of a substrate 10 whereon acomposite dielectric may be formed. Substrate 10 may comprise asemiconductor substrate in the case when a gate dielectric is to beformed or a bottom electrode when a capacitor is to be formed. A firstprecursor is chemisorbed on substrate 10 forming a first monolayer 14 asshown in FIG. 1. FIG. 1A shows an enlarged view of a portion ofsubstrate 10 and first monolayer 14 from FIG. 1. FIG. 1A shows in agraphical representation, not by way of limitation, individual moleculesof the first precursor chemisorbed to substrate 10. The individualmolecules may have one or more reactive sites 12, depending upon theparticular precursor.

A second precursor is reacted with the chemisorbed first precursor toform a product monolayer 16 on substrate 10 as shown in FIG. 2. Productmonolayer 16 is a reaction product of the first and second precursors.FIG. 2A shows in a graphical representation, not by way of limitation,individual molecules of the second precursor reacted and bonded to thechemisorbed first precursor molecules. Bonding may occur to firstmonolayer 14 at one or more of reactive sites 12. The reacted secondprecursor forms, at least in the graphical representation, a secondmonolayer 22. Depending on the particular precursors, reaction of thesecond precursor with the chemisorbed first precursor can change thecomposition of individual molecules comprised by first monolayer 14.Accordingly, first monolayer 14 is represented in FIG. 2A as changed toa reacted first monolayer 24.

Although not shown graphically in the Figures, the second precursor canmerely react with the first precursor, but not chemisorb additionalmaterial to first monolayer 14. Such would be the case when the secondprecursor cleaves some portion of the chemisorbed first precursorleaving reacted first monolayer 24 without second monolayer 22 formedthereon. Reacted first monolayer 24 may thus form a completed productlayer 16 or an additional precursor may be used to add material toreacted first monolayer 24, forming product layer 16.

Exposure of the chemisorbed layers to the first and second precursors,or different precursors, can be repeated forming successive firstmonolayers 14 and second monolayers 22 to provide a dielectric layer 18as shown in FIG. 3. In the context of HfCl₄ as a first precursor and H₂Oas a second precursor, HfCl₄ chemisorbs to substrate 10, excessprecursor is purged, and H₂O reacts with the chemisorbed precursor,releasing HCl and forming HfO₂ on substrate 10. For illustrationpurposes, second monolayer 22 in FIG. 2A can represent the oxygen fromH₂O included in the HfO₂ of product layer 16. Even so, those of ordinaryskill will recognize that it may be more technically accurate todescribe the oxygen as becoming a part of the original chemisorbed HfCl₄monolayer given the substitution of oxygen for chlorine purged from thesubstrate as a reaction byproduct along with hydrogen from the H₂O. Inthe context of La(thd)₃ as a precursor chemisorbed on substrate 10, asimilar mechanism may take place where the oxygen of H₂O forms La₂O₃ andthe (thd)₃ and hydrogen from H₂O are purged as reaction byproducts.

In accordance with the various aspects of the invention herein,dielectric layer 18 can be a composite dielectric that includes bothhafnium oxide and lanthanum oxide. A top electrode (not shown) can beformed over dielectric 18 in the case where substrate 10 is a bottomelectrode to create a capacitor construction. Also, as shown in FIG. 4,dielectric layer 18 may be processed according to the knowledge of thoseskilled in the art to form a transistor with a word line constructionincluding dielectric layer 18 as a gate dielectric, gate 20, and sidewall spacers 26. Notably, the aspects of the invention described hereinare applicable to a variety of transistor and capacitor constructions inaddition to those shown and/or described herein. The aspects of theinvention are particularly valuable in forming gate and capacitordielectrics in small geometries.

Accordingly, a still further aspect of the invention includes acomposite dielectric having alternate monolayers of hafnium oxide andlanthanum oxide over a substrate. As an example, the dielectric caninclude a plurality of single hafnium oxide monolayers interspersedamong a plurality of single lanthanum oxide monolayers. Alternatively,the dielectric can include a plurality of hafnium oxide multilayersinterspersed among a plurality of lanthanum oxide multilayers, themultilayers containing multiple monolayers.

Also, another aspect of the invention includes a composite dielectrichaving alternate monolayers of crystalline hafnium oxide and crystallinelanthanum oxide over a substrate. The monolayers may exhibit theproperty of being thermally stable at one atmosphere pressure and 20° C.temperature.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A composite dielectric forming method comprising atomic layerdepositing alternate layers of hafnium oxide and lanthanum oxide over asubstrate.
 2. The method of claim 1 wherein the method comprises formingone hafnium oxide monolayer, forming one lanthanum oxide monolayer, andrepeating to form a plurality of single hafnium oxide monolayersinterspersed among a plurality of single lanthanum oxide monolayers. 3.The method of claim 1 wherein the method comprises separately formingmultiple hafnium oxide monolayers creating a hafnium oxide multilayer,separately forming multiple lanthanum oxide monolayers creating alanthanum oxide multilayer, and repeating to form a plurality of hafniumoxide multilayers interspersed among a plurality of lanthanum oxidemultilayers.
 4. The method of claim 1 wherein the hafnium oxidecomprises HfO₂ and the lanthanum oxide comprises La₂O₃.
 5. The method ofclaim 1 wherein the hafnium oxide comprises thermally stable,crystalline hafnium oxide.
 6. The method of claim 1 wherein thelanthanum oxide comprises thermally stable, crystalline lanthanum oxide.7-24. (canceled).
 25. A composite dielectric comprising alternatemonolayers of hafnium oxide and lanthanum oxide over a substrate. 26.The dielectric of claim 25 comprising a plurality of single hafniumoxide monolayers interspersed among a plurality of single lanthanumoxide monolayers.
 27. The dielectric of claim 25 comprising a pluralityof hafnium oxide multilayers interspersed among a plurality of lanthanumoxide multilayers, the multilayers comprising multiple monolayers. 28.The dielectric of claim 25 wherein the hafnium oxide comprises HfO₂ andthe lanthanum oxide comprises La₂O₃.
 29. The dielectric of claim 25wherein the hafnium oxide comprises thermally stable, crystallinehafnium oxide and the lanthanum oxide comprises thermally stable,crystalline lanthanum oxide.
 30. A transistor comprising a gatedielectric containing the composite dielectric of claim
 25. 31. Acapacitor comprising a capacitor dielectric containing the compositedielectric of claim
 25. 32. A composite dielectric comprising alternatemonolayers of crystalline hafnium oxide and crystalline lanthanum oxideover a substrate, the monolayers exhibiting the property of beingthermally stable at 1 atmosphere pressure and 20° C. temperature. 33.The dielectric of claim 32 comprising 10-90 atomic percent (at. %)hafnium oxide and 10-90 at. % lanthanum oxide.
 34. The dielectric ofclaim 32 comprising 25-75 at. % hafnium oxide and 25-75 at. % lanthanumoxide.
 35. The dielectric of claim 32 comprising approximately 50 at. %hafnium oxide and approximately 50 at. % lanthanum oxide.
 36. Thedielectric of claim 32 wherein the hafnium oxide comprises HfO₂ and thelanthanum oxide comprises La₂O₃.